This application generally relates to turbine engines, and more particularly, to a variable stator vane.
A turbine engine typically includes multiple compressor stages. Circumferentially arranged stators are positioned axially adjacent to the compressor blades, which are supported by a rotor. Some compressors utilize variable stator vanes in which the stators possess inboard and outboard journals or trunnions supporting axial rotation. The high pressure compressor case supports outboard variable vane trunnions or OD trunnions while a segmented split ring supports inboard variable vane trunnions or ID trunnions.
Each stator vane includes an airfoil that extends between inner and outer platforms, or buttons. Trunnions extend from each of the platforms and are supported for rotation by the inner and outer cases. In one type of variable stator vane, a leading edge of the airfoil is inset relative to the circumferences of the platforms. A trailing edge of the airfoil extends beyond, or overhangs, the circumferences of the platforms. The transition area between the airfoil and the platforms must be designed to minimize stress.
One approach to minimize stress in the stator vane is to provide a transition fillet between the airfoil and the platforms. A fillet extends between the airfoil and each platform from the point where the airfoil trailing edge overhangs the circumference and wraps around the leading edge to the opposite side of the airfoil, terminating where the airfoil overhangs the circumference on the adjacent side. Stator vanes are still subject to stress in this transition area despite the use of fillets.
Another approach, which is sometimes used in combination with the above approach, is to make a single relief cut or slab-cut interfacing the trailing edge. An additional transition fillet is then applied to the slab-cut and the interfacing airfoil trailing edge. The slab-cut fillet adjoins the airfoil fillet, producing a continuous blend between the airfoil and its respective platforms. Structural optimization balances slab-cut material removal against fillet size and trailing edge overhang. Excessive trailing edge overhang often required for aerodynamic efficiency, is not conducive to structural optimization resulting in a variable vane susceptible to stress risers.
What is needed is a variable stator vane that includes features for minimizing the possibility of forming stress risers in transitional areas between the overhanging portion of the airfoil and the platforms during manufacture of the stator vane.